I did this with my brothers 69 Dart at the Martin CC. Its a warmed over 360/auto and typically ran 12.80's. At friday t&t I pulled the headers and jetted up two and ran best of 12.71 with a spinning 60ft. Saturday I put the 3" flowmasters that cut out before the rear end back on, left the jets alone and was dialing high 12.80's again. Weather was warmer but it gave me a baseline.